What is the evidence that sound travels as a wzq27himqi17 :jmv p/xave?

What is the evidence thatl yg oayekv.utt5h u..mdp5ep*8 : 50e sound is a form of energy?

Children sometimes play with a homemade “telephone” by attaching a s r-qjcac,f 73+ma3pz;zji o6rrlvy75tring to the bottoms of two paper cups. When the string is stretched and a child speaks into one cup, the sound can be heard at the other cup (Fig. 12–29). Explain clearly how thzcvoyr pr3f6j +l;c,m-jq 5a3r7a i7ze sound wave travels from one cup to the other.

When a sound wave passes from air into water, do you exp44b .+:cd mj1lc/xwzwt pyjv;ect the frequency or wavel wmlyb1ctx4/vj dpc:;wz.+ j4ength to change?

What evidence can you give that the speed o2taz61+0emx1 rx rfmg f sound in air does not depend significantly on frequency0t2az xreg 1m1 +6rfxm?

The voice of a person who has inhaled helium sounds very h s ou 2v mb0z7 v1/gx) (;9iay,spbguxrz8o2nkigh-pitched. Why?

How will the air temperature in a room affect the pitch of orga.u affsb;r6 -ep;-rwvn pipes?

Explain how a tube might be use i-m 5rii*z7rld as a filter to reduce the amplitude of sounds in various frequency ranges. (An example is a car mufflerl* i- 7r5irmiz.)

Why are the frets on a guitar (Fig. 12–30) spaced closer togg3mo)z 7+h/8qbt e byqether as you move up the fingerb+)bh7 o/qbm3qtzg 8 yeoard toward the bridge?

A noisy truck approaches you from behind a building. Initially you hear it b2w- t7j,ktaicmktz(( .7 gtlzut cannot see it. When it emerges and you do see it, its sound is suddenly “brighter” — you hear more of the high-frequency noise. Explain. [Hint: See Section 11–15 on diff(m.i2tg j,7zzkw7k t(t-l a tcraction.]

Standing waves can be said to be due to “interferenhk-xb2 b.xm* kc8a h(r(b3+ hxf6ceqmce in space,” whereas beats can be said to (h8kx *rbebq c ba2+c-.m 6(fhhkm3xxbe due to “interference in time.” Explain.

In Fig. 12–16, if the frequency of the speakers were lowered, 1ur 3cc1c -jhswould the points D and C (where destructive and constructive inhc-sccj 1ur31 terference occur) move farther apart or closer together?

Traditional methods of protectiq)k7rlz0u506j j rbaqng the hearing of people who work in areas with very high noise levels have consisted mainly of efforts to block or reduce noise levels. With a relatively new technology, headphones are worn that do not block the ambient noise. Instead, a device is used which detects the noise, inverts it electronically, then feeds it to the headphones in addition to the ambient noise. How could adding more nois0lqa jzkr 7u5j)rb06qe reduce the sound levels reaching the ears?

Consider the two waves sh;zoho ,7wc9 fxrpec797 o,qwhown in Fig. 12–31. Each wave can be thought of as a superposition of two sound waves withcxqh,eo7ow ;7p 79r,z9wch fo slightly different frequencies, as in Fig. 12–18. In which of the waves, (a) or (b), are the two component frequencies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if the source and observer move in the same direc;t i mvam 4ifk2.a45baa9e nj(tion, ajmb ( ;t4na 5 a4mvak2feii.9with the same velocity? Explain.

If a wind is blowing, will this a.: ayxq)j oo: u3ebyw5d:e, xvlter the frequency of the sound heard by a person at rest with respect to the source? Is the wavelength or vx,d:beoeqyxwo:)5 ua: v.y3 j elocity changed?

Figure 12–32 shows various positions of a child in motion on a swing. A-42v3 ne:dn saeebp v3 monitor is blowing a whis:d2vba -3 sv en4pn3eetle in front of the child on the ground. At which position, A through E, will the child hear the highest frequency for the sound of the whistle? Explain your reasoning.

  A hiker determines the length of a lake by listening for the 6drt (5qu7wbo i +*w)uovzn5uecho of her shout reflected by a cliff at the far end of the lake. She hears the echo 2.0 s after shouting. Estimate the 575*6 u(o w wq+dz nrio)uuvbtlength of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship just below the waterline. 3.aagypqiv)(7k ddy 4He hears the echo of the sound reflected from the ocean floor directly below 2.5 s later. How deep is the ocean at this point? Assume the speed of sound in seawater is 1560 q(7y3. dpa ia)yk 4gdvm/s (Table 12–1) and does not vary significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wavelengthi ql,e teo3 g-d,a)ai81mn:r hs in air at 20 $^{\circ} $ C for sounds in the maximum range of human hearing, 20 Hz to 20,000 Hz. $\lambda_{20Hz}$ =    m $\lambda_{20kHz}$ =    $ \times10^{-2 }$ m(b) What is the wavelength of a 10-MHz ultrasonic wave?    $ \times10^{ -5}$m

  An ocean fishing boat is drifting just above a schoof d(ub7gm1 t7foi/c+wc njp:2l of tuna on a foggy day. Without warning, an engine backfire occurs on another bo u72 c+podgb njf:t fm/wc71(iat 1.0 km away (Fig. 12–33). How much time elapses before the backfire is heard (a) by the fish,    s (b) by the fishermen?    s

  A stone is dropped from the top of a cliff. The splash it makes when sc ajb/n1eqak5 -xce-nhzuzi) (0tye n24s1-ztriking the water below is heard 3.5 s later. How high i 2jnyik0ec e45c-1(bqzsz)ut/ ha-azx1 n-ens the cliff?    m

  A person, with his ear to the ground, sees a huge stone strike the con76nhna:wr *wey 4zjc 2crete pavement. A moment w6rzh247j*n yea:c wn later two sounds are heard from the impact: one travels in the air and the other in the concrete, and they are 1.1 s apart. How far away did the impact occur? See Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error made over one milyg)p./,tyxuw e of distance by the “5-second rule”y) pu xtyw,g/. for estimating the distance from a lightning strike if the temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound at the pain level of 120 dB? hjzlsnwywr x81k ) 8vl;0qn9)   W/$m^2$Compare it to that of a whisper at 20 dB.    $ \times10^{-10 }$W/$m^2$

  What is the sound level of a souno.i 3clr35ue sd whose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB when fired s 9qb.yhs3492* 6 g(0iijuoaogdw zb32 vlgtj simultaneously at a certain place, what will behd9t2*a63buw(g29 is .ls ovqo 3jb gji4y zg0 the sound level if only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distance from an ai4hk2jxkiwg 21 :v6wlp rplane with four equally noisy jet engines is experiencing a sound level bordering on pain, 120 dB. What sound level would this person experience if the captain shut down all but one engine? [Hint: Addv : xg 2kw16lhj2pkwi4 intensities, not dB’s.]    dB

  A cassette player is said to have a signal-to-noise ratio of 58 dB, whereas9 smw,f k0 xfpfw5)ti5 for a CD player it is 95 dB. What is the ratio of intensities o )fim 5tww,pf9x5skf0f the signal and the background noise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output of sound from a person speaking in nor rx.euf8tc67cc ):/* c;gxg4vxxc 6d*bmxdp hmal conversation. Use Table 12–2. Assume the sound spreads roughly un6d r):hxmcfxv6/c cegg; p. x78*cbxc4 d*tuxiformly over a sphere centered on the mouth. $\approx$    $ \times10^{ -6}$W(Round to the nearest integer)
(b) How many people would it take to produce a total sound output of 100 W of ordinary conversation? [Hint: Add intensities, not dB’s.]$\approx$    $ \times10^{7}$people

  A 50-dB sound wave strikes an09g,(r vwmmwzqqwj pi7 /c4m2 eardrum whose area is $5 \times10^{ -5} m^2$ (a) How much energy is absorbed by the eardrum per second?    $ \times10^{-12}$W (b) At this rate, how long would it take your eardrum to receive a total energy of 1.0 J?   $ \times10^{ 3}$yr

  Expensive amplifier A is rated at 250 W, while the more modest amplifw)*vo3bc+vd s ccrr 84u4c1ifier B is rated at 4 wcsc*rrfuocc4v1b4dv 3i+)8 0 W. (a) Estimate the sound level in decibels you would expect at a point 3.5 m from a loudspeaker connected in turn to each amp.$I_{250}$ =    dB $I_{40}$ =    dB (b) Will the expensive amp sound twice as loud as the cheaper one?

  At a rock concert, a dB meter raahd3z.ft * e x7zel1/vs.7ymegistered 130 dB when placed 2.8 m in front of a loudspeaker on the stagedl1ex7 v.aht 3esma/.fy z*z7.
(a) What was the power output of the speaker, assuming uniform spherical spreading of the sound and neglecting absorption in the air?$\approx$    $ \times10^{2 }$W(“Round to one decimal place)
(b) How far away would the sound level be a somewhat reasonable 90 dB?   $ \times10^{2}$m

  Human beings can typicallyo05-wkbo uoo0 k: gnx/ detect a difference in sound level of 2.0 dB. What is the ratio of the amplituk0 w: oou/ox0ok5nbg -des of two sounds whose levels differ by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a) *pt ;fq dk+ /8f,soqoagb05elb u(i(vby what factor will the intensity increase? Increass/d 0 t( afl (*8iqebf,+ogkvoq p;b5ue by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplitudes, but onr9. wi nq:c3*,yennzve has twice the freque9ne,n:3 *qy. ivwzcn rncy of the other. What is the ratio of their intensities?   

  What would be the sound level (in dB) of at.g; rd6c g:wa sound wave in air that corresponds to a displacement amplitude of via;t gwg.6 crd:brating air molecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound level to seem as loud ljj4 h)jzi6bu1a4;a cas a 100-Hz tone that has a 50-dB sound la6u14ja;)j zchb4ij l evel? (See Fig. 12–6.)    dB

What are the lowest and highest fjhred7 ;j:kq/k sx0 +nrequencies that an ear can detect when the sound level is 3edx;k/ +j0shqn 7:jrk 0 dB? (See Fig. 12–6.)

  Your auditory system can accommodate a huge range of sound levels. What is the rh7iebfl93o .fuz rw3+ atio of highf 9hubw+i 7 3zleofr3.est to lowest intensity at
(a) 100 Hz,$ \times10^{ a }$ a =   
(b) 5000 Hz? $ \times10^{ a }$ a =   
(See Fig. 12–6.)

  The A string on a violin has a fundamental frequency of 440 Hz. The length oo.gni1u h *l0kf the vibrating portion is 32 cm, and it has a mass of 0.35 g. Under what tension must the string be plao.lg i*uhn k10ced?    N

  An organ pipe is 112 cm long. What are the fundamental an djr*cw;mb0s c5-kjhkkh4:d94 5goyzd first three audible overtones if the *h0w dj;oysm -5 cz:k jk94cbkh54dgrpipe is
(a) closed at one end, $f_{1}$ =    Hz $f_{3}$ =    Hz $f_{5}$ =    Hz $f_{7}$ =    Hz
(b) open at both ends?$f_{1}$ =    Hz $f_{2}$ =    Hz $f_{3}$ =    Hz $f_{4}$ =    Hz

  (a) What resonant frequency would you expect from blowing across the t. u8(rryt(c y18ffb ehop of an empty soda bottle that is 18 cm deep, if youe 8ycbyu81r(( f.htrf assumed it was a closed tube?    Hz (b) How would that change if it was one-third full of soda?   Hz

  If you were to build a pipe organ winsoyac ,81e rnqv001 fdx3q q2th open-tube pipes spanning the range of human hearing (20 Hz to 20 kHz), what would q2v3o c1ynrsf,q q0 d10na 8exbe the range of the lengths of pipes required? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string hasm-ix w)ihqk28iyrv4j r : )b2c a frequency of 540 Hz as its third harmonic. What will be its fundamental frequency if it is fii4 i 28br ci:ry-xqv)k2 h)mjwngered at a length of only 60% of its original length?   Hz

  An unfingered guitar string is 0.73 m long and is tuned to pl 2n w 1czbl-p(jvz 7qbf47-vimay E above middle C (330 Hz).bzplv 72vfz-q4 cmi7b1- n (jw
(a) How far from the end of this string must the finger be placed to play A above middle C (440 Hz)?$\approx$    m
(b) What is the wavelength on the string of this 440-Hz wave? $\approx$    m
(c) What are the frequency and wavelength of the sound wave produced in air at 20°C by this fingered string?    Hz    m

  (a) Determine the length of an open orgajhc: 3vjcri6 3*1kvp ;fxm y43 axtqd(n pipe that emits middle C (262 Hz) when the temperaturha1fpkjy xr(; c x*i363cvj:43tmq d ve is 21 $^{\circ} $ C.    m
(b) What are the wavelength and frequency of the fundamental standing wave in the tube?    Hz    m
(c) What are $\lambda$ and $f$in the traveling sound wave produced in the outside air?    Hz    m

  An organ is in tune atl 8npc21* bkxm 20 $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiece of the flute in Example 12–10 swpmhot/i(sei1 0;vq( 4h:g hwhould the hole be that must be uncovered to play D above middle C atoht wg1w/0q his:pme4(v;i (h 294 Hz?    m

  (a) At T = 20 $^{\circ} $C how long must an open organ pipe be to have a fundamental frequency of 294 Hz?    m
(b) If this pipe is filled with helium, what is its fundamental frequency?   Hz

  A particular organ pipe can resonate arpq --+ce b4xft 264 Hz, 440 Hz, and 616 Hz, but not at any other frequencies in between.p qfb4r -c+ex- (a) Show why this is an open or a closed pipe. ----待选择----closedopen  (b) What is the fundamental frequency of this pipe?   Hz

  A uniform narrow tube 1.80 m long is open at both*.r n x)p:tdqp wdu6a, ends. It resonates at two successive harmonics of frequencies 27.da)6 dn ,rtppx *qu:w5 Hz and 330 Hz. What is
(a) the fundamental frequency,    Hz
(b) the speed of sound in the gas in the tube?$\approx$    $ \times10^{2 }$ m/s

  A pipe in air at 20 zfocth vtvh1y.q:;gg o1647z) r h2c m$^{\circ} $ C is to be designed to produce two successive harmonics at 240 Hz and 280 Hz. How long must the pipe be, and is it open or closed?  ----待选择----closedopen  f =    m

  How many overtones are present within the audibu8- h atpyw6o9le range for a 2.14-m-long organ p8yw hto 6apu-9ipe at 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximately 2.5 cm long. It is open to the outs8k:j+u6m cqqxr*t 9bs 8dv3reide and is closed at the other end by the eardrum. Estimate the frequencies (in the audible range) of the standing waves in the ear ca* ursc:mtvq3 xk8je89d+b 6rqnal. What is the relationship of your answer to the information in the graph of Fig. 12–6? $f_1$ =    Hz $f_3$ =    Hz $f_5$ =    Hz

  A piano tuner hears one beat every 2.0 s ejb8trq0k )h)when trying to adjust two strings, one of bq8e h0r)k)t jwhich is sounding 440 Hz. How far off in frequency is the other string? ±    Hz

  What is the beat frequency if middle C ( h4 7ke( m-bi. ye;fwhoen5vh9262 Hz) and $C^＃$ (277 Hz) are played together?    Hz What if each is played two octaves lower (each frequency reduced by a factor of 4)? $\approx$    Hz

  A certain dog whistle operates at 23.5 kHz, while another lknby/r3fbuln13;n jj)3jis z(l(9 x(brand X) operates at an unknown frequency. If neither whistle can be heard by humans whef((yr 1 9ljbl;u3)ln3 b3jxs /jn izknn played separately, but a shrill whine of frequency 5000 Hz occurs when they are played simultaneously, estimate the operating frequency of brand X.    kHz

  A guitar string produces 4 beats/s when sounded with a 350-Hz tuning fork and9t1 xfv7 wi1eqjl7:pg 9 beats/s when sounded with a 355-Hz tuning fork. What is the vibrational frequency of the string? Explain your reasoning. iltqjfp 1 7wxgev7 9:1   Hz

  Two violin strings are tuned to the same frequenrn ql.t5, a6l:3 q8, dyhgtq5ii2 rabycy, 294 Hz. The tension in one string is then decreased by 2.0%. What will be the beat fra 3 hq8qtyt2ai 5g5y,b6.linrrq:ld ,equency heard when the two strings are played together? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be heard if two identical flutes each try to play middle C sc(,rfgf :/pn(262 Hz), but one is cf /(: ,fngsrpat 5.0°C and the other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. Fork B has a frequency of 441 H4co0jhpr:nw0t 6,r)dla -vy pz; when A and B are sounded togethenjry- 4ad w,0ctpo)r:0vpl 6hr, a beat frequency of 3 Hz is heard. When B and C are sounded together, the beat frequency is 4 Hz. What are the possible frequencies of A and C? What beat frequencies are possible when A and C are sounded together?$f_A$ =    Hz or    Hz
$f_C$ =    Hz or    Hz
|$f_A$-$f_C$|    Hz or    Hz

  Two loudspeakers are 1.80 m apart. A d2t 7uex( afo4person stands 3.00 m from one speaker and 3.aftxd o e42u7(50 m from the other.
(a) What is the lowest frequency at which destructive interference will occur at this point? f =    Hz
(b) Calculate two other frequencies that also result in destructive interference at this point (give the next two highest). Let T = 20 $^{\circ} $C $\approx$    Hz $\approx$    Hz

  Two piano strings are supposed to be vibrating at 132 Hz, bu60ck( 5pqaks bt a piano tuner hears three beats every 2.0 s when they are played together. (a) If one is vibrating at 1a5qc0k6p bk s(32 Hz, what must be the frequency of the other ?   Hz    Hz
(b) By how much (in percent) must the tension be increased or decreased to bring them in tune?   % increase    %decrease

  A source emits sound oya.1a+ l*eft s/j q4vrf wavelengths 2.64 m and 2.76 m in air. How many beats per second will be heard? (. 4 eyjv/1rf*slqa+t aAssume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fir7+kvi u-v4554bd ajwdj0cx h ge engine’s siren is 1550 Hz when at rest. What frequency do you detect if you move with a s04bjkd-c5v j v4d+5g h7ua wixpeed of 30 m/s
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing still. What frequency dqpio /er* wz9:q( khw(o you detect if a fire engine whose siren emits at 1550 Hz moves at a z*orwhei/(qq: 9pw( kspeed of 32 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequency if a 2000-Hz sou(fwplu/a .+p)( t 6sbtqno: yyrce is moving toward you at 15 m/s versus you moving toward it at 15 m/s Are the two frequencies exactly the same? Are they clof p)obnu:yt y/ (.p6 (ltwas+qse? $f'_{source\,movine}$    Hz
$f'_{observe\,movine}$    Hz
(b) Repeat the calculation for 150 m/s and then again
$f'_{source\,movine}$    $ \times10^{ 3}$Hz
$f'_{observer\,movine}$    $ \times10^{ 3}$Hz
(c) for 300 m/s What can you conclude about the asymmetry of the Doppler formulas?$f'_{source\,movine}$    $ \times10^{ 3}$Hz
$f'_{observer\,movine}$    $ \times10^{ 3}$Hz

  Two automobiles are equipped with the same single frequency horn. When one in7jvcjc1 5 ab665gig ps at rest and the other is moving toward the first at 15 m/s the driver at rest hears a beat frequency of 5.5 Hz. What is the frequenvjcgi16b6 pa n5g5j7c cy the horns emit? Assume T = 20 $^{\circ} $C    Hz

  A bat at rest sends out ultrasonic sound waves at 1rkox92/1zl2* mqg ,tgo mfhd50.0 kHz and receives them returned from an object moving directly away from it at 25 m/s What is the received sound flhx r m1*2k/o 2, mtzg9gqfod1requency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a )+f83 4agccc-xpt9vp6 9 jyialk a4xsspeed of 5 m/s As it flies, the bat emits an ultrasonic sound wave wif6c9t kp-y+8va4s ag4pj3i)c xl 9ax cth frequency 30.0 kHz. What frequency does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppleryoj6bnj:-n g pa.h,5xiy0ag + experiments, a tuba was played on a moving flat train car at a frequency of 75 Hz, and a second identical tuba played the same tone while at rest in the railway station. What beat frequency was heard if the trn+oa6 i xg,hn.:5ajy0pygj b -ain car approached the station at a speed of 10 m/s ?   Hz

  A Doppler flow meter uses ultrasound waves to measure blood-flx wb yu-vy*ha 6bkv(a 8.0c7* ubna:vzow speeds. Suppose the device emits sound at 3.5 MHz, and the speed of sound in human tissue is taken to be 1540 m/s What is the expected beat frequency if blood is flowing in large leg arteries at 2 cm/s directly away from the sbv7( 8z0auwyya* babvk v. n6 x:ch-u*ound source?   Hz

  The Doppler effect using ultrasoner1bbro8g; 0h+.od z qic waves of frequency $2.25 \times10^{ 6}$Hz is used to monitor the heartbeat of a fetus. A (maximum) beat frequency of 500 Hz is observed. Assuming that the speed of sound in tissue is $1.54 \times10^{3 }$ m/s calculate the maximum velocity of the surface of the beating heart.    m/s

  A factory whistle emits sound of frequency 570 Hz. When theevu3ca 3xjx:z5 r8 z8m wind velocity is 12 m/s from the north, what frequency will oza8mj 338xur:5ezcvx bservers hear who are located, at rest,
(a) due north,   Hz
(b) due south,   Hz
(c) due east,    Hz
(d) due west, of the whistle? What frequency is heard by a cyclist heading    Hz
(e) north    Hz
(f) west, toward the whistle at 15 m/s?   Hz
Assume T = 20 $^{\circ} $C

  How fast is an object fy3asv(kpuq i (8j5m- w* t0zlmoving on land if its speed at 20 $^{\circ} $C is Mach 0.33?    m/s
(b) A high-flying jet cruising at 3000 km/h displays a Mach number of 3.2 on a screen. What is the speed of sound at that altitude?    m/s

  An airplane travels at Mach 2.3 where t2 +cbza-xvt n48 lzw;xhe speed of sound is 310 m/s (a) What is the angle the shock wave makes wit;v+tz8wbx2n4 x alc z-h the direction of the airplane’s motion?    $^{\circ} $
(b) If the plane is flying at a height of 7100 m, how long after it is directly overhead will a person on the ground hear the shock wave? $\approx$    s (Round to the nearest integer)

  A space probe enters the thin atmosphere of a planet)je/8th w wce2 where the speed of sound is only about 35 m/s c/eh tww )ej82
(a) What is the probe’s Mach number if its initial speed is 15000 km/h$\approx$    (Round to the nearest integer)
(b) What is the angle of the shock wave relative to the direction of motion?    $^{\circ} $